During these college years he was often restless and weary of duty, inclined to indolence, and an early riser with the greatest difficulty. These things he overcame in later life. He had some religious doubts, which completely vanished as he studied and thought more deeply.
In 1819 Arnold removed to Laleham, with his mother, sister, and aunt, and remained here for the next nine years, preparing private pupils for the universities.
A year after coming to Laleham, he married, when he was twenty-five, Mary, youngest daughter of the Rev. John Penrose, in Nottinghamshire, and sister of one of his best college friends, Trevenen Penrose. She was a worthy helper through all the laborious years which followed.
Although Arnold had fitted himself for the Church, he loved the work of teaching. He wrote to a friend about to engage in a similar occupation. "I know it has a bad name, but my wife and I always happened to be fond of it.... I enjoyed and do enjoy the society of youths of seventeen or eighteen; for they are all alive in limbs and spirits at least, if not in mind, while in older persons the body and spirits oftener become lazy and languid without the mind gaining any vigor to compensate for it....
"The misery of private tuition seems to me to consist in this, that men enter upon it as a means to some further end; are always impatient for the time when they may lay it aside; whereas, if you enter upon it heartily as your life's business, as a man enters upon any other profession, you are not then in danger of grudging every hour you give to it....
"I should say, have your pupils a good deal with you, and be as familiar with them as you possibly can. I did this continually more and more before I left Laleham, going to bathe with them, leaping, and all other gymnastic exercises within my capacity, and sometimes sailing or rowing with them. They, I believe, always liked it, and I enjoyed it myself like a boy, and found myself constantly the better for it."
"Large private schools," he thought, "the worst possible system; the choice lies between public schools, and an education whose character may be strictly private and domestic."
The home at Laleham was very dear to him. Here six of his children were born. He loved the quiet walks along the banks of the Thames, his garden back of his house, where, he said, "there is always something to interest me even in the very sight of the weeds and litter, for then I think how much improved the place will be when they are removed," and the churchyard, where in after years his mother, his infant child, and now his distinguished son Matthew are resting.
One of his pupils at Laleham thus writes of Arnold: "His great power as a private tutor resided in this, that he gave such an intense earnestness to life. Every pupil was made to feel that there was a work for him to do,—that his happiness as well as his duty lay in doing that work well.... His hold over all his pupils perfectly astonished me. It was not so much an enthusiastic admiration for his genius or learning or eloquence which stirred within them; it was a sympathetic thrill caught from a spirit that was earnestly at work in the world....